<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .red{     
            /* 背景颜色 */
            background-color: red;
        }
        .green{   
            background-color: greenyellow;
        }
        .box{
            width: 150px;
            height: 100px;
        }
    </style>
</head>
<body>
    <div class="red box">红色</div>
    <div class="green box">绿色</div>
    <div class="red box">红色</div>
</body>
</html>